1. Field of Inventions
The present invention relates to an illumination device for illuminating a certain region-to-be-illuminated with light emitted from a point-like light source and a lens employed in he illumination device, being applied to an illumination devices for electronic-flash-illumination in for portable phones, digital cameras, video cameras or others, or to illumination devices for book-reading illuminators, map illuminators or the likes, and to lenses employed in the devices.
In general, the present invention can be broadly applied to illumination devices which are used for supplying illumination light to a certain limited region-to-be-illuminated like a region corresponding to an object such as subject for photography, and to lenses employed in them for controlling light traveling directions.
2. Related Arts
It is known well to have image-pickup-devices such as portable phones, digital cameras or video cameras be equipped with so-called strobo illumination device for electronic flash illumination as to enable image-pickup in night or dark locations to be available.
It is noted that “strobo illumination” is defined as illumination” using a light source providing light emission synchronized with image pickup. Illumination devices for such uses are required to have ability of illuminating an object-to-be-illuminated (such as a subject for photography) illuminatively and uniformly.
FIG. 21 shows a conventional illumination device used for providing illuminative and uniform illumination, which is disclosed in Document 1 noted below. Referring to FIG. 21. illumination device 101, used for book-reading illuminators or map illuminators, provided illumination light that is supplied to a limited area (i.e. region-to-be-illuminated) such as book-reading surface or map surface. LED 102 is employed as a light source, emitting light which is supplied to a region-to-be-illuminated via lens 103.                Document 1; Tokkai-2005-174685 (JP)        
However, if illumination device 101 shown in FIG. 21 is applied to an image pickup device, a problem arises. That is, some of emission rays (irradiation rays) H from emission face 107 of lens 103 cross each other within a region which can be illuminated by illumination device 101, providing crossover portion 104 which looks illuminative locally and gives a reduced evenness of illumination.
Saying more concretely, crossover portion 104 looking like a ring-like illuminative portion emerges in surface-to-be-illuminated 108 which passes crossover portion 104 and extends in parallel with reference plane 106 shown in FIG. 21, causing surface-to-be-illuminated 108 to have a reduced degree of illuminance uniformity.